The purpose of this study is to evaluate the effectiveness and safety of tramadol hydrochloride (HCl) 37.5 miligram (mg)/acetaminophen 325 mg compared to gabapentin in participants with diabetic neuropathic (nerve disorder caused by diabetes mellitus) pain.

Change From Baseline in Pain Intensity Score at Day 43 [ Time Frame: Baseline and Day 43 ] [ Designated as safety issue: No ]

Pain intensity was assessed on 11-point numerical rating scale ranging from 0=no pain to 10=pain as bad as you can imagine.

Secondary Outcome Measures:

Percentage of Participants With Pain Relief [ Time Frame: Day 15, Day 29 and Day 43 ] [ Designated as safety issue: No ]

Pain relief was assessed on a scale ranging from -1 to 4, where -1=became worse, 0=no change, 1=relieved a little, 2=relieved moderately, 3=relieved a lot and 4=completely resolved.

Overall Assessment of Study Medication by Participants [ Time Frame: Day 43 ] [ Designated as safety issue: No ]

Overall assessment of study medication was done by participants. Assessment was made on a scale of -2 to 2 where, -2=very bad, -1=bad, 0=no change, 1= good and 2=very good.

Overall Assessment of Study Medication by Investigator [ Time Frame: Day 43 ] [ Designated as safety issue: No ]

Overall assessment of study medication was done by Investigator. Assessment was made on a scale of -2 to 2 where, -2=very bad, -1=bad, 0=no change, 1= good and 2=very good.

Change From Baseline in Brief Pain Inventory (BPI) Score at Day 43 [ Time Frame: Baseline and Day 43 ] [ Designated as safety issue: No ]

The BPI is a questionnaire designed to assess the severity and impact of pain on quality of life. Pain severity score is caculated by sum of all severity items (pain worst, pain least, pain average and pain now) divided by pain now. Total score for pain severity ranges from 0=no pain to 10=extreme pain. Pain interference score was calculated by sum of all interference items (general activity, mood, walking ability, normal work, relations with other people, sleep, and enjoyment of life) score. Total score for pain interference ranges from 0=no interference to 70= interferes completely.

Change From Baseline in Short Form-36 (SF-36) Score at Day 43 [ Time Frame: Baseline and Day 43 ] [ Designated as safety issue: No ]

The SF-36 is designed to assess the health status of participants. The SF-36 includes 1 multi-item scale measuring physical health and mental health. Physical health includes physical functioning, role limitations due to physical health, pain and general health. Mantal health includes role limitations due to emotional problems, energy/fatigue, emotional well being and social functioning. Each item is scored on a 0-100 range so that the lowest and highest possible scores are set at 0 and 100, respectively. All items are scored so that a high score defines a more favorable health state.

Participants will receive 1 tablet containing tramadol HCl 37.5 milligram (mg) and acetaminophen 325 mg once daily, at bed time on Days 1 to 3, 1 tablet twice daily on Days 4 to 7 and 1 tablet thrice daily on Day 8 to 14. If there is no pain relief, the dosage can be increased up to 8 tablets per day for Days 15 to 28. The increased dose will be maintained for Days 29 to 42.

Drug: Tramadol hydrochloride/ Acetaminophen

Participants will receive 1 tablet containing tramadol HCl 37.5 milligram (mg) and acetaminophen 325 mg once daily, at bed time on Days 1 to 3,. 1 tablet twice daily on Days 4 to 7 and 1 tablet thrice daily on Day 8 to 14. If there is no pain relief, the dosage can be increased up to 8 tablets per day for Days 15 to 28. The increased dose will be maintained for Days 29 to 42.

Other Name: Ultracet

Active Comparator: Gabapentin

Participants will receive Gabapentin 300 mg once daily at bed time on Day 1, 300 mg twice daily on Day 2 and 300 mg thrice daily on Day 3. Gabapentin 300 mg will be administered twice daily (in the morning and midday) and gabapentin 600 mg in the evening on Day 8 to 14. If there is no pain relief, the dosage can be increased up to 3600 mg per day for Days 15 to 28. The increased dose will be maintained for Days 29 to 42.

Drug: Gabapentin

Participants will receive Gabapentin 300 mg once daily at bed time on Day 1, 300 mg twice daily on Day 2 and 300 mg thrice daily on Day 3. Gabapentin 300 mg will be administered twice daily (in the morning and midday) and gabapentin 600 mg in the evening on Day 8 to 14. If there is no pain relief, the dosage can be increased up to 3600 mg per day for Days 15 to 28. The increased dose will be maintained for Days 29 to 42.

Detailed Description:

This is an open-label (a medical research study in which participants and researchers are told which treatments the participants are receiving, "unblinded"), multi-center and randomized (study drug is assigned by chance) study to compare the effectiveness and safety of tramadol HCl 37.5 mg/acetaminophen 325 mg with gabapentin in participants with diabetic neuropathy. The study will consist of 4 periods: Screening period (up to Day -14), Randomization period (Day 1), Dosage adjustment period (Day 15) and Maintenance period (Day 43). The participants will be randomly assigned to 1 of the 2 treatment groups: tramadol HCl 37.5 mg/acetaminophen 325 mg or gabapentin. Tramadol Hcl/acetaminophen group will receive 1 tablet for 3 days, then 1 tablet twice daily for 4 days followed by 1 tablet thrice daily for next 7 days. If there is no pain relief, the dosage can be increased up to 8 tablets per day for Day 15 to 28, and then the increased dosage will be maintained for Day 29 to 42. Gabapentin group will receive 300 mg on Day 1, 300 mg twice daily on Day 2, and 300 mg thrice daily for Day 3 to 7. Then for Day 8 to 14, participants will receive 300 mg in the morning, 300 mg in the midday and 600 mg in the evening. If there is no pain relief, gabapentin can be increased up to 3600 mg per day for Day 15 to 28, and then the increased dosage will be maintained for Day 29 to 42. Primarily, efficacy will be evaluated by pain intensity using numeric rating scale (NRS). Participants' safety will be monitored throughout the study.

Eligibility

Ages Eligible for Study:

18 Years to 75 Years (Adult, Senior)

Genders Eligible for Study:

Both

Accepts Healthy Volunteers:

No

Criteria

Inclusion Criteria:

Participants having painful symmetric neuropathy (a disturbance in the function of the brain or spinal cord that may affect the nerves and muscles of the body) in the lower limbs applicable to both of the following conditions: decreased sensation of leg to monofilament, none or decreased ankle reflexes or decreased vibratory sensation and pain symptoms such as numbness (loss of sensation), tingling, paresthesia (a skin sensation, such as burning, prickling, itching, or tingling, with no apparent physical cause), burning, shooting pain, stabbing or lancinating (characterized by a sensation of cutting, piercing, or stabbing) pain

Participants having painful diabetic neuropathy in the lower limbs for 3 months before randomization

Participants with physical damage or disease which may cause abnormal absorption, excessive accumulation, metabolism or excretion disorder of the study medication

Contacts and Locations

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study.
To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT00634543